"""Async SQLAlchemy engine, session factory, and declarative base.

Works with SQLite (aiosqlite) or Postgres (asyncpg) depending on DATABASE_URL.
"""

from collections.abc import AsyncGenerator

from sqlalchemy import event
from sqlalchemy.ext.asyncio import (
    AsyncSession,
    async_sessionmaker,
    create_async_engine,
)
from sqlalchemy.orm import DeclarativeBase

from app.core.config import settings


class Base(DeclarativeBase):
    """Declarative base shared by all models."""


engine = create_async_engine(settings.database_url, echo=settings.debug, future=True)

if engine.sync_engine.dialect.name == "sqlite":

    @event.listens_for(engine.sync_engine, "connect")
    def _set_sqlite_pragma(dbapi_connection, connection_record) -> None:
        """WAL mode lets readers/writers avoid blocking each other; busy_timeout
        makes a connection wait for a lock instead of immediately raising
        "database is locked" (the pysqlite/aiosqlite default is 0ms).
        """
        cursor = dbapi_connection.cursor()
        cursor.execute("PRAGMA journal_mode=WAL")
        cursor.execute("PRAGMA busy_timeout=5000")
        cursor.close()


AsyncSessionLocal = async_sessionmaker(
    engine,
    class_=AsyncSession,
    expire_on_commit=False,
    autoflush=False,
)


async def get_db() -> AsyncGenerator[AsyncSession, None]:
    """FastAPI dependency yielding a request-scoped session."""
    async with AsyncSessionLocal() as session:
        yield session


async def init_db() -> None:
    """Create all tables. Convenient for dev/SQLite and tests.

    In production prefer Alembic migrations (``alembic upgrade head``).
    """
    # Import models so they register with Base.metadata before create_all.
    import app.models  # noqa: F401

    async with engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)